Steam Rotary Joints vs Thermal Oil Rotary Joints: Key Differences

Two Media, Very Different Challenges

Both steam and thermal oil carry heat to industrial equipment — drying ovens, calenders, reactors, heat exchangers. But the way they behave at high temperature creates fundamentally different demands on rotary joints.

Choosing the wrong joint type leads to premature seal failure, leaks, and safety hazards. Here’s how to get it right.

Temperature Profiles

Steam

• Saturated steam: 100–180°C at typical industrial pressures (0.1–1.0 MPa)
• Superheated steam: 180–300°C+ in process heating applications
• Challenge: Temperature is directly tied to pressure. Higher temperature = higher pressure = more stress on seals.

Thermal Oil

• Typical operating range: 150–300°C
• Challenge: Temperature is independent of pressure (oil systems are typically low-pressure). But oil degrades at high temperature, creating varnish and carbon deposits.

Key difference: Steam joints must handle both high temperature AND high pressure. Thermal oil joints handle high temperature but low pressure.

Seal Material Requirements

Steam Applications

• Primary seal material: Carbon with anti-scaling treatment
• Secondary option: Silicon carbide for superheated steam above 200°C
• Critical concern: Scale formation. Steam condenses on cool surfaces, depositing mineral scale on seal faces. This is the #1 cause of steam joint failure.
• Solution: The RTH series uses a balanced seal design with external springs that resist scale buildup. The reduced contact pressure allows scale particles to pass rather than embed.

Thermal Oil Applications

• Primary seal material: Carbon or specialized graphite compounds
• Secondary option: Tungsten carbide for extreme temperatures
• Critical concern: Carbon varnish. Oil breaks down at high temperature, forming sticky carbon deposits on seal faces.
• Solution: The RTQ series is specifically designed for thermal oil with a seal geometry that minimizes dead zones where oil can stagnate and degrade.

Pressure Considerations

Steam

• Operating pressure: 0.1–1.6 MPa (typical)
• Must handle pressure fluctuations and water hammer
• Safety critical: steam joint failure can cause burns
• RTH series rating: Up to 1.6 MPa — suitable for most steam applications

Thermal Oil

• Operating pressure: 0.05–0.5 MPa (circulation pumps)
• Low pressure but high temperature
• Oil leaks are fire hazards, not pressure hazards
• RTQ series rating: Up to 0.5 MPa — optimized for oil circulation systems

Installation Differences

Steam Joint Installation

• Must be installed at the highest point of the rotating equipment (steam rises)
• Requires a steam trap downstream to remove condensate
• Needs insulation to prevent heat loss and condensation
• Should include a flexible connector to absorb thermal expansion

Thermal Oil Joint Installation

• Can be installed at any position (oil flows by pump pressure)
• Requires proper piping to prevent oil stagnation
• Should include a drain valve for maintenance
• Insulation recommended but not critical for function

Maintenance Comparison

Aspect	Steam Joint	Thermal Oil Joint
Primary maintenance	Scale removal	Varnish cleaning
Inspection frequency	Monthly	Quarterly
Seal replacement interval	1–2 years	2–3 years
Common failure mode	Scale buildup → seal face damage	Varnish → seal face sticking
Critical fluid quality	Water treatment (softening)	Oil temperature control

Selection Decision Tree

Choose a steam joint (RTH series) when:

• Your medium is saturated or superheated steam
• Operating temperature is 100–250°C
• Pressure is 0.1–1.6 MPa
• You need reliable operation with standard water treatment

Choose a thermal oil joint (RTQ series) when:

• Your medium is thermal oil (HTF)
• Operating temperature is 150–300°C
• Pressure is below 0.5 MPa
• You need long service life with minimal oil degradation concerns

Can One Joint Handle Both?

In theory, a well-designed joint can handle both media. In practice, the optimal seal geometry differs:

• Steam joints benefit from tighter clearances to prevent condensate accumulation
• Oil joints benefit from wider clearances to prevent varnish buildup

For applications that switch between steam and oil (rare but existing), consult with the manufacturer for a custom solution.

Getting the Right Recommendation

Every application has unique conditions. The best approach is to share your operating parameters with an engineer who understands both media types.

Ruitus manufactures both steam-rated (RTH) and thermal oil-rated (RTQ) rotary joints, each optimized for its specific medium. Our engineering team can help you select the right model based on your exact temperature, pressure, and installation conditions.

Contact us for a free recommendation.